A wide variety of welding processes are used to join sheet metal panels or other types of parts together. Laser welding is one type of welding process that offers advantages such as the ability to weld from one side without requiring access to the back side of the parts to be welded as is required for spot or resistance welding. Laser welding also may be performed without a filler wire like manual inert gas (MIG) welding or tungsten inert gas (TIG) welding. Laser welding eliminates maintenance of weld tips, electrodes and torches.
Welding parts that are coated with an anticorrosion layer of zinc or a zinc based coating composition creates problems for laser welding processes because the coating has a lower melting point than a steel substrate panel. When the coating is heated during a laser welding operation, the coating vaporizes creating smoke plumes and gaseous emissions. Plumes of smoke are removed from the path of the laser by blowing air across the welding area. Gaseous emissions from vaporizing the coating applied to an area of two parts that are assembled together in a face-to-face relationship must be permitted to escape from between the panels or the gaseous emissions may bubble up through the molten laser weld and create porosity in the weld.
It has been proposed to provide a series of protuberances, or bumps, between panels through the use of a “humping effect” wherein a laser is used to heat the inner surface of one of two panels that are to be joined together. After the panels are placed face-to-face with the protuberances between the panels, a laser weld is formed through one side of the assembly while off-gassing from the coating is emitted through a space between the panels created by the bump shaped protuberances. One problem with bump shaped protuberances is that it is difficult to consistently control the height of the bumps.
Another problem with laser welding panels arranged in a face-to-face relationship is that the weld may have increased porosity at the tail end of the weld. Porosity in the weld is unacceptable if the porosity affects more than a specific length of the weld. Laser welds that replace spot welds are generally configured in a C-shape that is less than 9 mm in diameter and have a curved length of 25 mm. If excessive porosity is encountered, there is insufficient space for extending the length of the C-shaped weld.
This disclosure is directed to solving the problems of facilitating off-gassing coatings and assuring weld quality by reducing weld porosity, and other problems relating to laser welding.